Tremulant effect for electronic musical instruments



May 10, 1966 R. H. PETERSON 3,250,845

TREMULANT EFFECT FOR ELECTRONIC MUSICAL INSTRUMENTS Filed July 1, 1963 TONE Z 0-1 AMPLIFIER 105:, G E N EEATO I? KEVBOQPD JQ/ T k: M

j07 TONE AMPLIFIER GENEPATOR I xevaoneo I 5 United States Patent 3,250,845 TREMULANT EFFECT FOR ELECTRONIC MUSICAL INSTRUMENTS Richard H. Peterson, 10108 Harnew Road E,

Oak Lawn, Ill. Filed July 1, 1963, Ser. No. 291,927 8 Claims. (Cl. 84-1215) My invention relates to musical instruments particularly to improvements in the tremulant effects obtainable on such instruments. The word tremulant is used in a general way to refer to the well-known periodic variation in pitch, amplitude, tone quality, or other characteristic of musical tone. This effect is commonly produced by electronic means, by frequency modulating, amplitude modulating, or phase modulating the signals produced by the oscillators or other tone sources of an electronic musical instrument. Sometimes a combination of amplitude and frequency modulation is employed and the combination appears to create a more desirable type of tremulant than either frequency modulation or amplitude modulation alone. Another approach to the problem of creating a desirable tremulant effect has been to impose the desired tremulant rate modulation on a signal by means of rotating loud speakers, or rotating sound channels, or sound reflectors associated with fixed loud speakers. The best known example of such mechanical tremulant devices is shown in the patent to Donald 1. Leslie, Re. 23,323. As will be further discussed hereinafter, all of the presently known systems have some limitations or disadvantages; and it is therefore an object of this invention to provide an improved tremulant system that is capable of superior performance from an esthetic point of view.

In the accompanying drawings:

FIGURE 1 is a partial block diagram and partial schematic circuit diagram showing one form of the invention;

FIGURE 2 is a similar drawing showing another form of the invention.

It is generally agreed that electronic organs do not have the same esthetic appeal as do pipe organs. One of'the reasons for this is that electronic organs generally use one or at least a rather limited number of tone generators or banks of signal producing devices, from which many stops are simultaneously derived. When tremulant effects are created by simply modulating these signals, it is not surprising that the effect on the listener is different than the effect created by a pipe organ consisting of many complete ranks of pipes, each individual pipe of which responds somewhat differently to the variation in wind pressure that is the basic source or cause of the tremulant effect in the pipe organ. In other words, when listening to a pipe organ, many pipes are ordinarily sounding simultaneously, each of which is experiencing changes in pitch, amplitude, and tone quality and wherein the magnitude of these different effects may be very different for each of the simultaneously sounding notes. The total effect is one of great complexity and the resulting chorus effect is highly desirable. Acoustic tremulants, such as those produced by the previously mentioned rotating loud speakers or rotating sound channels are for most effects generally superior to the simpler electronically accomplished modulation. This is because the acoustic devices produce complex modulations due partly to the multiple paths by which the sound must reach the listener after it leaves the rotating device. It should be understood that the rotating type tremulant producers cause frequently modulation of the sound by virtue of the well-known Doppler principle, and that they also produce amplitude, phase, and tone quality modulation because of the constantlyichanging source of the sound.

Acoustic tremulant devices, however, are most successwords, with tones in the flute family).

fulwith tone qualities of very simple nature (in other Ice This is because theacoustic tremulant devices generally produce different amounts of frequency modulation at different frequen ciesoftentimes, for example, producing a much more pronounced frequency modulation at high frequencies where the physical dimensions of the rotating sound channel are large compared to the wave length of the sound, and at the same time producing a much lesser degree of modulation at lower frequencies where the wave length may be many times greater than the dimensions of the rotor.

This is undesirable where a complex wave is to be reproduced by the acoustic tremulant system because the harmonics of the tone are subject to a very different tremulant treatment than the fundamental and lower order harmonics. In a pipe organ, or in any acoustic instru ment, it is obvious that when the pitch of the tone produc ing device is shifted, it is necessarily true that all of the harmonics and the fundamental must shift in pitch simultaneously and to the same degree. It is very unnatural if, as in the case of the rotor, the harmonics are shifted to a greater degree than the fundamental.

Another disadvantage of the acoustic tremulant systems is that for the rotor to be effective or for a rotating loud speaker to provide an effective amount of tremulant, the radius of the circle described by the rotating speaker or by the mouth of the sound channel must be a substantial part of a wave length of the tonebeing reproduced by the system. At the low frequencies produced by conventional musical instruments, rotors with diameters of several feet are sometimes required.

Apparatus according to this invention'overcomes the afore mentioned limitations of acoustic tremulant systems by superimposing the modulation effects produced by the acoustic devices with electrically produced modulation, synchronized with the rotation of the rotary apparatus.

In the embodiment of the invention selected for illustration, and referring first to FIGURE 1, I have indicated at a conventional tone generator, which may be any of the many types known to those skilled in the art and which, for example, may be a plurality of oscillators such as those shown in the Patent 2,649,006. The tone generator is associated with the key board 101 in such a manner that operating the keys will cause selected tone signals to appear at the output terminal 103 of the tone generator. At 105, I have shown a terminal the potential of which determines the pitch of the signals produced by the tone generator 100 to the degree that if a voltage varying at a tremulant rate is applied to terminal 105, the pitch of the signals appearing on output terminal 103 will be frequency modulated at the tremulant rate. Reference character 107 is a conventional ampliher and may include tone filters and similar circuitry that is usual in a complete electric organ system. Associated with the amplifier 107 is loud speaker 108, which is associated with the rotating sound channel 110, which may be, for example, similar to that described in the aforementioned Leslie patent. The motor 112 is coupled to the rotor through the belt 114 and the pulley 116, so as to effect rotation of the rotor around the axis 118, with the'result that the signal produced by loud speaker 108, will be subject to the expected frequency, amplitude, phase and tone quality modulation that is characteristic of such rotating tremulant devices.

Coupled to the rotor shaft 118 is a variable density disc 120, interposed between the stationary light source 122, and the photo-resistor 124. The battery and the switch 128, are connected in such a manner that when switch 128 is closed the battery will supply power to the lamp and the lamp will emit a flood of light on to the disc 120. Photo-resistor 124 may be any of several types of photo-resistor as for example the cadmium sulphide 3 type. One suitable type is marketed by the Amperex Corp. and is known as an ORP-60.

A portion of the battery voltage is applied to vibrato terminal of the tone generator by means of a voltage divider consisting of the photo-resistor 124 and the resistor 126. Since the photo-resistor has a resistance the value of which is dependent upon the illumination that the photo-resistor receives, it is apparent that the rotation of the variable density disc will cause the resistance of photo-resistor 124 to vary at a tremulant rate and thus cause a varying voltage to appear at terminal 105 of the tone generator, thus producing a frequency vibrato in the signals appearing at output terminal 163.

At 144, I have shown a second photo-resistor associated with the same disc 120 and with a second lamp 140, which is connected to the battery through switch 142. When switch 142 is closed, the photo-resistor 144 will be subject to the fluctuating light from lamp through the disc 120 and the photo-resistor 144 is used as an element in the signal frequency voltage divider consisting of resistor 144 and resistor 146. When the resistance of the photo-resistor 144 is varying, it is apparout that the amplitude of the signal appearing at amplifier input terminal 148 will also vary, or in other words, will be amplitude modulated.

Connected across photo-resistor 144, I have shown the switch 150 and the capacitor 152. When switch 153 is closed, high-frequency components of the signals at tone generator output terminal 103 will be shunted across the varying resistance of photo-resistor 144 and will therefore be subject to little or no amplitude modulation while frequencies of a lower order will be subject to a relatively greater amplitude modulation.

Similarly, it should be noted that it is a simple matter in the design of the individual oscillators comprising tone generator 100 to provide means whereby a given voltage fluctuation at the vibrate terminal 105 will produce a relatively large vibrato effect at certain frequencies (for example low frequencies) and a relatively lesser or no vibrato at higher frequencies. Thus, it can be seen that a combined tremulant effect is produced wherein the desirable qualities of the mechanical tremulant are realized but without the undesired characteristics. Furthermore, the essential desirable qualities can be realized with rotors much smaller than those previously used.

Referring now to FIGURE 2, I have shown a block diagram of a similar system, but wherein phase modulation is electrically produced by means of the phase shift type tremulant represented by the circuitry enclosed in the dotted line rectangle 176, plus the photo-resistor 182. The theory of operation of phase-shift tremulants and of their similarity to pitch vibrate systems is described more fully in the US. Patent No. 2,835,814 to Richard E. Dorf dated May 20, 1958.

Signals appearing at the output terminal 103 of the tone generator are applied to transformer 174, which acts as a phase splitter and which produces signals that are out of phase atterminals 176 and 178 respectively with respect to ground. If a signal of one phase (for example the signal appearing at terminal 176) is connected to the amplifier input terminal 148 through a capacitor 180, and if an identical signal but of opposite phase (such as that appearing at transformer terminal 178) is applied to amplifier input terminal 148 through photo-resistor 182, the phase of the resultant signal appearing at 148 will vary depending upon the relative magnitudes of the capacitive reactance 180 as compared to the resistance of photo-resistor 180. When the switch 183 is closed battery 130 will release the lamp 184 to supply a flood of light, which, when modulated by the disc 120, will cause the resistance of photo-resistor 182 to vary at vibrato frequency with the result that the phase modulation will be produced on the signal applied to amplifier 148. It should be understood that the particular mechanical tremulant device 110, the particular phase modulation system illustrated, and the particular method of amplitude modulation and of frequency modulation that have been described are only illustrative of the many similar systems known in the art. This application is a continuation in part of my co-pending application Serial Number 116, filed January 4, 1960, now Patent 3,229,019, dated January 11, 1966.

In some cases it has been found that it is useful to adjust the phase relationship between the electrical modulation and the modulation produced by the rotor, so that from a normal listening position the two modulation effects are additive. This can be readily accomplished in the examples cited by adjusting the position of the rotor mouth with respect to the dark area on the variable density disc 12%). in other cases, particularly where rather mild tremulant effects are desired, the phasing is not too significant and perfect synchronizing is not required. Others may readily adapt the invention for use under various conditions of service, by employing one or more of the novel features disclosed, or equivalents thereof. As at present advised with respect to the apparent scope of my invention, I desire to claim the following subject matter.

1. in an electrical musical instrument, a source of electrical signals; a loudspeaker operatively associated with said source; a first modulating means comprising a mechanical tremulant device associated with said loudspeaker for modulating the signals emanating therefrom; a second modulating means for electrically modulating said electrical, signals, and means for at least substantially synchronizing the first and second modulating means.

2. An electrical musical instrument according to claim 1 where the second modulating means produces amplitude modulation.

3. An electrical musical instrument according to claim 1 where the second modulating means produces frequency modulation.

4. An electrical musical instrument according to claim 1 where the second modulating means produces phase modulation.

5. An electrical musical instrument according to claim 1 where the second modulating means produces a combination of two or more types of modulation.

6. An electrical musical instrument according to claim 1 where the eifectiveness of the second modulating means is a function of frequency.

7. An electrical musical instrument according to claim 1 in which the phase relationships of the modulations produced by the first and second modulating means are such as to produce a greater degree of etfective modulation of the signal than that produced by either the first or the second modulating means.

8. All electrical musical instrument according to claim 1 in which said electrical modulating means is relatively more effective at low frequencies than at high frequencies, and said mechanical modulating means is relatively more effective at high frequencies than at low frequencies; whereby the use of both in suitable proportions can approximate the overall performance of an acoustic instrument.

References Qited by the Examiner FORETGN PATENTS 249,391 8/ 1962 Australia.

ARTHUR GAUSS, Primary Examiner. D. D. FORRER, Assistant Examiner. 

1. IN AN ELECTRICAL MUSICAL INSTRUMENT, A SOURCE OF ELECTRICAL SIGNALS; A LOUDSPEAKER OPERATIVELY ASSOCIATED WITH SAID SOURCE; A FIRST MODULATING MEANS COMPRISING A MECHANICAL TREMULANT DEVICE ASSOCIATED WITH SAID LOUDSPEAKER FOR MODULATING THE SIGNALS EMANATING THERERFROM; A SECOND MODULATING MEANS FOR ELECTRICALLY MODULATING SAID ELECTRICAL SIGNALS, AND MEANS FOR AT LEAST SUBSTANTIALLY SYNCHRONIZING THE FIRST AND SECOND MODULATING MEANS. 